Takeuchi F, Iwahori K, Kamimura K, Sugio T
Administration Center for Environmental Science and Technology, Okayama University, 3-1-1 Tsushima Naka, Okayama 700-8530, Japan.
J Biosci Bioeng. 1999;88(4):387-92. doi: 10.1016/s1389-1723(99)80215-1.
Fifty iron-oxidizing bacteria isolated from natural environments were screened for resistance to mercuric ions (Hg2+). Thiobacillus ferrooxidans Funis 2-1, the strain found to show the greatest resistance to Hg2+ among the fifty isolates, gave a cell yield of 7.0 x 10(7) cells/ml after 8 d cultivation in an Fe2+-medium (pH 2.5) containing 0.7 microM Hg2+. Funis 2-1 volatilized 80% of the total mercury added to the medium over 8 d of cultivation. T. ferrooxidans AP19-3, more sensitive to Hg2+ than Funis 2-1, could not grow in an Fe2+-medium (pH 2.5) containing 0.7 microM Hg2+ even over a 28 d cultivation period. When resting cells of strains Funis 2-1 and AP19-3 were incubated for 3 h in a salt solution containing 0.7 microM Hg2+ (pH 3.0), 14.3% and 7.9% of the total mercury added to the reaction mixtures respectively, were volatilized. The activity of the mercuric reductase from Funis 2-1 was only 2.8 times higher than that of the enzyme from AP19-3. Since the markedly higher mercury resistance of Funis 2-1 compared with that of AP19-3 cannot be explained only by the level of the mercuric reductase activity, the levels of mercury resistance of iron oxidase and cytochrome c oxidase were studied. The 1 microM mercuric ions inhibited the 35% of iron-oxidizing activity from AP19-3. In contrast, the same concentration of Hg2+ did not inhibit the activity of iron oxidase from Funis 2-1. In the case of the cytochrome c oxidases purified from both strains, the 0.2 microM Hg2+ inhibited approximately 40% of cytochrome c oxidizing activity from AP19-3, on the contrary, the activity of the enzyme from Funis 2-1 was activated 1.8- and 1.2-fold, respectively, in the presence of 0.08 and 0.2 microM Hg2+. Since cytochrome c oxidase is one of the most important components of the iron-oxidizing system, these results indicate that both the existence of cytochrome c oxidase resistant to Hg2+ as well as that of mercuric reductase in the cells is responsible for the more rapid growth of Funis 2-1 than that of in an Fe2+-medium containing 0.7 microM Hg2+.
从自然环境中分离出50株铁氧化细菌，检测它们对汞离子（Hg2+）的抗性。在50株分离菌中，氧化亚铁硫杆菌Funis 2-1对Hg2+的抗性最强，在含有0.7微摩尔Hg2+的Fe2+培养基（pH 2.5）中培养8天后，其细胞产量为7.0×10(7)个细胞/毫升。在8天的培养过程中，Funis 2-1将添加到培养基中的总汞的80%挥发掉。氧化亚铁硫杆菌AP19-3对Hg2+比Funis 2-1更敏感，即使在28天的培养期内，也无法在含有0.7微摩尔Hg2+的Fe2+培养基（pH 2.5）中生长。当Funis 2-1和AP19-3菌株的静止细胞在含有0.7微摩尔Hg2+（pH 3.0）的盐溶液中孵育3小时时，分别有14.3%和7.9%添加到反应混合物中的总汞被挥发。Funis 2-1的汞还原酶活性仅比AP19-3的酶活性高2.8倍。由于Funis 2-1与AP19-3相比明显更高的汞抗性不能仅用汞还原酶活性水平来解释，因此研究了铁氧化酶和细胞色素c氧化酶的汞抗性水平。1微摩尔汞离子抑制了AP19-3 35%的铁氧化活性。相比之下，相同浓度的Hg2+并未抑制Funis 2-1的铁氧化酶活性。对于从这两种菌株中纯化的细胞色素c氧化酶来说，0.2微摩尔Hg2+抑制了AP19-3约40%的细胞色素c氧化活性，相反，在存在0.08和0.2微摩尔Hg2+的情况下，Funis 2-1的该酶活性分别被激活了1.8倍和1.
